C++ 实现自定义类型的迭代器操作

template<class _Category,
 class _Ty,
 class _Diff = ptrdiff_t,
 class _Pointer = _Ty *,
 class _Reference = _Ty&>
 struct iterator
 { // base type for iterator classes
 typedef _Category iterator_category;
 typedef _Ty value_type;
 typedef _Diff difference_type;
 typedef _Diff distance_type; // retained
 typedef _Pointer pointer;
 typedef _Reference reference;
 };

// ITERATOR STUFF (from <iterator>)
// ITERATOR TAGS (from <iterator>)
struct input_iterator_tag //只读
 { // identifying tag for input iterators
 };
struct _Mutable_iterator_tag //只写
 { // identifying tag for mutable iterators
 };
struct output_iterator_tag //只写
 : _Mutable_iterator_tag
 { // identifying tag for output iterators
 };
struct forward_iterator_tag //前向移动
 : input_iterator_tag, _Mutable_iterator_tag
 { // identifying tag for forward iterators
 };
struct bidirectional_iterator_tag //可双向移动
 : forward_iterator_tag
 { // identifying tag for bidirectional iterators
 };
struct random_access_iterator_tag //随机读写
 : bidirectional_iterator_tag
 { // identifying tag for random-access iterators
 };
//...

// TEMPLATE FUNCTION count_if
template<class _InIt,
 class _Pr> inline
 typename iterator_traits<_InIt>::difference_type
 _Count_if(_InIt _First, _InIt _Last, _Pr _Pred)
 { // count elements satisfying _Pred
 typename iterator_traits<_InIt>::difference_type _Count = 0;
 for (; _First != _Last; ++_First)
 if (_Pred(*_First))
  ++_Count;
 return (_Count);
 }

#include<iterator>
template<class T>
class MyIterator : public iterator<input_iterator_tag, T>{
 public:
 MyIterator(T* p){
  _ptr = p;
 }
 //赋值
 MyIterator& operator = (const MyIterator &iter)
 {
 _ptr = iter._ptr;
 }
 //不等于
 bool operator != (const MyIterator &iter)
 {
 return _ptr!= iter._ptr;
 }
 //等于
 bool operator == (const MyIterator &iter)
 {
 return _ptr == iter._ptr;
 }
 //前缀自加
 MyIterator& operator ++ ()
 {
 _ptr++;
 return *this;
 }
 //后缀自加
 MyIterator operator ++ (int)
 {
 MyIterator tmp= *this;
 _ptr++;
 return tmp;
 }
 //取值
 T& operator * ()
 {
 return *_ptr;
 }
 private:
 T* _ptr;//实际的内容指针，通过该指针跟容器连接
};

template<class T>
class myVector{
public:
 typedef MyIterator<T> iterator;//所有类型迭代器用同一个名字，便于写出更通用的代码
 myVector(){
 _selfElems = new T[32];
 _count = 32;
 init();
 }
 myVector(int n){
 _selfElems = new T[n];
 _count = n;
 init();
 }
 void init(){
 memset(_selfElems, 0, sizeof(T)* _count);
 }
 //常用接口
 T& operator[](int i){
 return _selfElems[i];
 }
 iterator begin(){
 return iterator(_selfElems);
 }
 iterator end(){
 return iterator(_selfElems + _count);
 }
 int size() const {
 return _count;
 }
private:
 T* _selfElems;
 int _count;
};

bool eq_10(int k){
 return k == 10;
}
int main(){
 //自定义类型
 myVector<int> mv(10);
 mv[3] = 10; mv[9] = 10;
 myVector<int>::iterator it = mv.begin();
 cout <<"mv:"<<endl;
 while (it != mv.end()){
 cout << *(it++) << " ";
 }
 cout << endl;
 cout << count_if(mv.begin(), mv.end(), eq_10) << endl;
 //STL 容器
 vector<int> v(10,0);
 v[3] = 10; v[9] = 10;
 vector<int>::iterator it1 = v.begin();
 cout << "v:" << endl;
 while (it1 != v.end()){
 cout << *(it1++) << " ";
 }
 cout << endl;
 cout << count_if(mv.begin(), mv.end(), eq_10) << endl;
 getchar();
 return 0;

//T为某种迭代器
template<class T>
void display(T it, T end){
 T it1 = it;
 while (it1 != end){
 cout << *(it1++) << " ";
 }
 cout << endl;
 cout << count_if(it,end, eq_10) << endl;
}
int main(){
 //自定义类型
 myVector<int> mv(10);
 mv[3] = 10; mv[9] = 10;
 //STL 容器
 vector<int> v(10, 0);
 v[3] = 10; v[9] = 10;
 //vector 和 myVector底层实现有很大区别，但是可用同一个函数做遍历等操作
 display(mv.begin(), mv.end());
 display(v.begin(), v.end());
 getchar();
 return 0;
}

#pragma once
//MyIterator.h
#include <iterator>
#include <exception>
template<typename Container>
class MyIterator :public std::iterator<std::random_access_iterator_tag, typename Container::value_type>
{
protected:
  Container& container;
  typename Container::iterator pos;
public:
  explicit MyIterator(Container& c) :container(c), pos(c.begin()){}
  MyIterator(const MyIterator& rhs) :container(rhs.container),pos(rhs.pos) {}
  MyIterator& operator =(const MyIterator& rhs)
  {
    throw_ex(rhs.container);
    pos = rhs.pos;
    return *this;
  }
  //--等就省略了...
  MyIterator& operator ++()
  {
    auto tmp = container.end() - 1;
    if (pos == tmp)
      ++pos;
    else
      pos += 2;
    return *this;
  }
  bool operator ==(const MyIterator& rhs)const
  {
    try
    {
      if (&rhs.container == &container)
        return pos == rhs.pos;
      else
      {
        throw exception("对象错误");
      }
    }
      catch (exception &e)
      {
        cout << e.what();
        exit(EXIT_FAILURE);
      }
    }
bool operator !=(const MyIterator& rhs)const
{
  return !(*this == rhs);
}
typename Container::value_type & operator *()
{
      return *pos;
}
void begin()
{
  pos = container.begin();
}
void end()
{
  pos = container.end();
}
private:
  void throw_ex(const Container& c)
  {
    try
    {
      if (&c == &container)
        return;
      else
        throw exception("Copy 构造失败");
    }
    catch (exception &e)
    {
      cout << e.what();
      exit(EXIT_FAILURE);
    }
  }
};
//无法使用或添加vector<T> vec 成员函数vec.begin()或全局函数begin(vec)
//我们做个假冒的全局函数 start(vec) over(vec)
template<typename Container>
MyIterator<Container> start(Container& c)
{
    MyIterator<Container> mi(c);
    mi.begin();
    return mi;
}
template<typename Container>
MyIterator<Container> over(Container & c)
{
    MyIterator<Container> mi(c);
    mi.end();
    return mi;
}

#include <iostream>
#include <vector>
#include "MyIterator.h"
#include <list>
using namespace std;
//因继承了iterator<std::random_access_iterator_tag,Container::value_type>才拥有此特性
template<typename Iterator>
void printIterator(const Iterator &It)
{
  cout << typeid(typename iterator_traits<Iterator>::iterator_category).name() << endl;
}
int main()
{
  vector<int> coll{ 1,2,3,4,5,6,7,8,9,10 };
  MyIterator<decltype(coll)> myit(coll);
  printIterator(myit);
  for (; myit != over(coll); ++myit)
  {
    cout << *myit << ends;
  }
  system("pause");
  return 0;
}